Two way transmitter-receiver array adaptation for multi-carrier code division multiplexed modulation with array-carrier MLE reception — A path modeled design

We propose in this paper a two-way wireless OFDM multi-carrier code-division multiplexed modulation with optimum transmitter-receiver broadband far-field antenna array adaptation to the propagation path characteristics. The frequency band is shared between the two directions with TDD and we assume the same array antenna is used at each station for transmission and reception. Employing a path model in the analysis, and assuming error-free measurement of the transmittances from the center of the transmitter station to the array elements of the receiver station, it is shown that the array-carrier MLE (Maximum Likelihood Estimate) reception of the code-division multiplexed symbols discriminates the paths with delay time difference greater than the inverse of the signal bandwidth or with sufficiently different directions of arrival. And as a result bandwidth-constrained path-wise matched reception is realized. It was confirmed by simulation assuming Rayleigh (not Rice) path model that the system gives substantially higher BER versus SNR per bit performance than that of the carrier-only MLE reception employing an omni-directional antenna or an array antenna only for the purpose of directivity. Because of the optimality of the reception the transmitter array adaptation has nothing to do but optimally to deliver transmitted power to the paths so as the total expected arriving power at the receiving station be maximum. Owing to the reciprocity of propagation by using the same antenna array for reception and transmission, the transmitter array adaptation makes use of the measurement, at the receiver, of the transmittance to derive the optimum transmitter array weightings. The algorithm at each station, achieves two way optimization without interchanging any data to be obtained by the channel measurement in the pilot periods.